Transfection is the process of introducing foreign particles such as nucleic acids (DNA, RNA, etc.) and proteins into the cell. Two fundamental goals of transfection are: i) to introduce the desired amount of target foreign particle(s) into the cells, thereby maximizing transfection efficiency, and ii) to preserve the health and life of the cells to the greatest extent, hence maximizing cell viability.
The general method of transfection is as follows: 1) Culture cells to desired cell density; 2) Transfect cells with method of choice, commonly calcium complexes, liposome complexes, or electroporation; and 3) Analyze transfected cells. Several common methods of transfection include liposome-mediated transfection, microinjection, calcium phosphate-based transfection, and electroporation.
Liposome-mediated transfection involves the enclosure of a nucleic acid within a lipid-based vesicle, which, as a nonpolar complex, facilitates its movement across the cell membrane and into the cell. Lipid-mediated transfection is widely used but, with many cell lines, it suffers from a low rate of transfer of foreign material into the cell. The lipid vesicles, or liposomes, are also toxic to cells at higher concentrations.
Microinjection is the use of a micro-needle to inject foreign material directly into the cell. It is a time-inefficient method of transfection when working with even moderately sized cell numbers.
Calcium phosphate-based methods involve the formation of a complex between DNA and calcium phosphate, which is then taken in by the cell. This method does not allow for an efficient uptake of foreign material across a wide variety of cell lines.
Electroporation involves the application of an electrical current to a mixture of cells so as to cause the opening of the cell membrane and subsequent entry of material into the cell through pores. Although it tends to allow for higher transfection efficiency than many other methods, electroporation can also be very harmful to the cell. Depending on the nature of the buffer as well as the degree and length of the electric shock, electroporation can cause the loss of greater than 90% of the starting population of cells.
Finding a buffer in which to electroporate cells without compromising cell viability is critical to the process of performing a transfection experiment. The following are commonly used electroporation buffers:                a) Buffers containing basic media or basic media supplemented with 10% serum. Although very commonly used, they tend to be of poor quality as electroporation buffers. They cause drastically diminished cell viability and low transfection efficiency.        b) Hypoosmolar buffers. These buffers are used on the premise that they cause the uptake of water into the cell prior to electroporation, thereby increasing cell volume and pore formation, which leads to improved transfection efficiency. Although modest gains in transfection efficiency and cell viability are achieved, there is a risk that the low osmolarity of the buffer will cause cell lysing, reducing cell viability.        c) Buffers of low ionic strength. Because of their diminished conductivity, these buffers impose less electrical stress on the cell due to reduced current flow in the solution. This is thought to minimize electrically-induced damage to the cells being transfected.        d) Buffers supplemented with DEAE-dextran. It is hypothesized that these buffers allow nucleic acids to associate loosely with the cell membrane, decreasing the distance the foreign particle has to travel to enter the cell, and allowing for higher transfer of material.        
The general disadvantages of the above described electroporation buffers include:                a) a failure to allow for high transfer of foreign material into the cell;        b) high cytotoxicity;        c) inconsistent performance with respect to transfer efficiency and/or cytotoxicity;        d) inability to be used with little modification across a wide variety of cell lines;        e) complex or time-consuming protocols.Thus, there remains a need in the art for electroporation buffers that provide for improved cell viability and increased transfection efficiency.        